Nac is fine to use. i would rec Bac over it though. bac is more than just heated water , the BA helps limit bacteria growth and why its added.
i would NEVER rec using tap water... you have any idea how much crap is in there? nvm the added floride + pharmaceuticals that are in the water (many medications come out in urine intact and not broken down), they dont filter that out, only the basics. shit i avoid even drinking tap water (in big city) because iv looked into it and its actually not very good for you. a water source out of a stream or spring that has also had some natural filtration + the man made filtration is best to drink and/or distill for injections. just my opinion though.